JP2011231637A - Alcohol concentration estimating device and fuel injection control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate an alcohol concentration of used fuel.SOLUTION: An engine 1 includes a combustion chamber 1d, an intake port 11a, an exhaust port 12a, an intake valve 13, an exhaust valve 14, an injector 2 injecting fuel into the intake port 11a, an ignition plug 3 igniting an air-fuel mixture in the combustion chamber 1d, and an air-fuel ratio sensor 80 provided upstream of a three way catalyst 8 arranged in an exhaust passage 12 for detecting an oxygen concentration in exhaust gas, and uses ethanol containing fuel as used fuel. The air-fuel sensor 80 is constructed to output an electric current according to the oxygen concentration in exhaust gas when applied with first application voltage VP1 and to decompose water contained in the exhaust gas when applied with second application voltage VP2. The ethanol concentration of the used fuel is estimated based on a difference between the output current IP2 when applied with the second application voltage VP2 and the output current IP1 when applied with first application voltage VP1.

Description

  The present invention relates to an alcohol concentration estimation device that estimates the concentration of alcohol contained in a fuel used, and a fuel injection control device for an internal combustion engine that includes the alcohol concentration estimation device.

  As internal combustion engines (also referred to as engines) for automobiles and the like, there are known flexible fuel internal combustion engines that can use a single fuel of alcohol (for example, methanol, ethanol, etc.) or a mixed fuel of alcohol and gasoline. A vehicle equipped with this type of engine is generally called a flexible fuel vehicle (FFV). By using alcohol fuel, environmental performance such as improved exhaust emissions and reduced fossil fuel consumption is achieved. It is trying to improve.

  In FFV, 100% gasoline fuel, mixed fuel of alcohol and gasoline, or 100% alcohol fuel can be used. Since the physical properties of alcohol are different from those of gasoline, it is necessary to perform fuel injection control, ignition timing control, etc. according to the concentration of alcohol (alcohol content) contained in the fuel used. Therefore, in order to appropriately perform fuel injection control, ignition timing control, and the like, it is important to accurately detect and estimate the alcohol concentration of the fuel used.

  Conventionally, various techniques for estimating the alcohol concentration of the fuel used have been proposed. For example, in Patent Document 1, after the fuel cut ends, based on an integrated amount calculated from a target value calculated by at least one of an air-fuel ratio (A / F) sensor and a sub oxygen sensor and an actual measurement value, It has been shown to estimate the alcohol concentration of the fuel used.

JP 2009-52477 A

By the way, if the alcohol concentration of the fuel used is different, the component ratio (concentration) of the combustible component in the exhaust gas will be different, and the sensor output (output current) of the air-fuel ratio sensor may fluctuate due to this. . Specifically, as the sensor output of the air-fuel ratio sensor, an output current (referred to as “original output current”) corresponding to the O ₂ concentration (oxygen concentration) in the exhaust gas should be output. However, depending on the difference in the concentration of combustible components (for example, H ₂ , CO, HC, C ₃ H _8, etc.) in the exhaust gas, an output current shifted from the original output current to the rich side or lean side can be output. There is sex. For example, when the concentration of H _{2 in} the exhaust gas increases, the output current of the air-fuel ratio sensor shifts to a richer side than the original output current. Conversely, when the concentration of C ₃ H ₈ in the exhaust gas increases, It shifts to the lean side from the original output current.

  However, conventionally, such variation in the output current of the air-fuel ratio sensor (deviation from the original output current) has not been considered. For this reason, there existed a problem that the estimation precision of the alcohol density | concentration of the fuel used worsened. Further, when fuel injection control (air-fuel ratio feedback control) is performed based on the output current of the air-fuel ratio sensor that varies as described above, there is a problem that the air-fuel ratio of the air-fuel mixture deviates from the target air-fuel ratio (for example, the theoretical air-fuel ratio). there were.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to suppress deterioration in estimation accuracy of alcohol concentration and deterioration in fuel injection control due to fluctuations in the output current of the air-fuel ratio sensor. And

  In the present invention, means for solving the above-described problems are configured as follows. That is, the present invention can inject fuel into a combustion chamber, an intake port and an exhaust port communicating with the combustion chamber, an intake valve and an exhaust valve that can open and close the intake port and the exhaust port, respectively, and an intake port or a combustion chamber. A fuel injection valve, an ignition plug for igniting the air-fuel mixture in the combustion chamber, and an air-fuel ratio sensor provided on the upstream side of the catalyst disposed in the exhaust passage for detecting the oxygen concentration in the exhaust gas. An alcohol concentration estimation device for an internal combustion engine as a fuel to be used, wherein the air-fuel ratio sensor outputs a current corresponding to an oxygen concentration in exhaust gas when the first applied voltage is applied, and the first When a second applied voltage higher than the applied voltage is applied, the water contained in the exhaust gas is decomposed, and the second output voltage when the second applied voltage is applied. And current based on the difference between the first output current when the first applied voltage is applied, is characterized by estimating the alcohol concentration of the fuel used. The alcohol-containing fuel is meant to include 100% gasoline fuel, mixed fuel obtained by mixing alcohol and gasoline, and 100% alcohol fuel.

  According to the above configuration, the difference in the output current is an increase in the output current of the air-fuel ratio sensor that is increased by the decomposition of the moisture in the exhaust gas. Therefore, the difference in the output current is the moisture concentration in the exhaust gas. It changes according to. Since the moisture concentration in the exhaust gas changes according to the alcohol concentration of the fuel used, the difference in the output current changes according to the alcohol concentration of the fuel used. In this way, in the above configuration, the alcohol concentration of the fuel used is estimated based on the difference in the output current that correlates with the moisture concentration in the exhaust gas, so the alcohol concentration is estimated based only on the first output current. Compared to the case, the alcohol concentration can be estimated with higher accuracy. That is, even if the first output current fluctuates due to the difference in the concentration (component ratio) of the combustible component in the exhaust gas, it is possible to suppress the deterioration in the estimation accuracy of the alcohol concentration due to this. In addition, the alcohol concentration can be estimated easily in a short time by simply raising the applied voltage to the air-fuel ratio sensor from the first applied voltage to the second applied voltage temporarily.

  In the alcohol concentration estimation apparatus of the present invention, ethanol can be used as the alcohol. That is, the fuel used for the internal combustion engine can be ethanol-containing fuel.

  In this configuration, since the ethanol concentration of the fuel used is estimated based on the difference between the output currents correlated with the moisture concentration in the exhaust gas, the ethanol concentration is estimated based on only the first output current. The ethanol concentration can be accurately estimated. That is, even if the first output current fluctuates due to the difference in the concentration of the combustible component in the exhaust gas, it is possible to suppress the deterioration in the estimation accuracy of the ethanol concentration due to this.

  The present invention also provides a combustion chamber, an intake port and an exhaust port communicating with the combustion chamber, an intake valve and an exhaust valve that can open and close the intake port and the exhaust port, respectively, and fuel can be injected into the intake port or the combustion chamber. A fuel injection valve, an ignition plug for igniting the air-fuel mixture in the combustion chamber, and an air-fuel ratio sensor provided on the upstream side of the catalyst disposed in the exhaust passage for detecting the oxygen concentration in the exhaust gas. A fuel injection control device for an internal combustion engine as a fuel to be used, comprising an alcohol concentration estimation device having the above-described configuration, and using an alcohol concentration estimated by the alcohol concentration estimation device, from an output current based on an oxygen concentration in exhaust gas The first output current shift amount is calculated, the first output current is corrected according to the calculated shift amount, and the first output current is corrected based on the corrected first output current. It is characterized by controlling the fuel injection amount by the fuel injection valve.

  In this configuration, the shift amount of the first output current of the air-fuel ratio sensor is calculated using the alcohol concentration of the fuel used estimated by the above-described alcohol concentration estimation device. That is, by using the alcohol concentration of the fuel used that is accurately estimated by the alcohol concentration estimation device, it is possible to accurately calculate the deviation amount of the first output current of the air-fuel ratio sensor. This makes it possible to make the output current of the air-fuel ratio sensor corrected based on the deviation amount as close as possible to a value corresponding to the actual air-fuel ratio. Then, by performing the air-fuel ratio feedback correction based on the corrected output current, it is possible to suppress the deterioration of the fuel injection control due to the deviation amount.

  In the fuel injection control device for an internal combustion engine of the present invention, from the alcohol concentration estimated by the alcohol concentration estimation device, the concentration of the combustible component in the exhaust gas at the alcohol concentration is obtained, and the concentration of the combustible component in the exhaust gas thus obtained is determined. It is preferable to calculate the shift amount of the first output current using

  Here, the deviation amount of the first output current of the air-fuel ratio sensor changes according to the concentration of the combustible component in the exhaust gas, and the concentration of the combustible component in the exhaust gas changes according to the alcohol concentration of the fuel used. To do. In this configuration, the shift amount of the first output current of the air-fuel ratio sensor is calculated using the alcohol concentration of the fuel used estimated by the above-described alcohol concentration estimation device. Therefore, the alcohol concentration of the fuel used can be accurately estimated based on the difference in the output current, and the concentration of the combustible component in the exhaust gas can be accurately obtained. As a result, the deviation amount of the first output current of the air-fuel ratio sensor can be accurately calculated. This makes it possible to make the output current of the air-fuel ratio sensor corrected based on the deviation amount as close as possible to a value corresponding to the actual air-fuel ratio. Then, by performing the air-fuel ratio feedback correction based on the corrected output current, it is possible to suppress the deterioration of the fuel injection control due to the deviation amount.

  In the fuel injection control apparatus for an internal combustion engine according to the present invention, the amount of deviation of the first output current is expressed by the following equation: IL = IP1 (X) −IP1 (0) (IL: deviation of the first output current) Amount, IP1 (X): the first output current when the fuel used is a fuel of alcohol X%, IP1 (0): the first output current when the fuel used is a fuel of alcohol 0%) It is preferable to be calculated by the following. The first output current IP1 (X) when the fuel used is a fuel of alcohol X% is expressed by the following equation: IP1 (X) = ΣA · (Do−Ki · Si · Di), (A: Proportional constant, Do: oxygen concentration in exhaust gas, i: number assigned to each combustible component in exhaust gas, Ki: chemical equivalent of combustible component i in exhaust gas, Si: output current of air-fuel ratio sensor stoichiometric The oxygen equivalent ratio of the combustible component i in the exhaust gas at the same time as the output, Di: the concentration of the combustible component i in the exhaust gas) is preferably calculated.

Here, (Do-Ki.Si.Di) of the combustible component i in the exhaust gas has the following value. O ₂ and the combustible component i in the exhaust gas flowing through the exhaust passage pass through the inside of the air-fuel ratio sensor (diffusion layer), reach the exhaust side electrode, and reach the exhaust side electrode and O ₂ and the combustible component. As a result of the reaction with i, a value representing the amount (concentration) of O ₂ or combustible component i remaining (remaining) on the exhaust-side electrode is (Do-Ki · Si · Di). The sum of (Do−Ki · Si · Di) of each combustible component i is a value representing the degree of excess or deficiency of O ₂ on the exhaust side electrode of the air-fuel ratio sensor. Specifically, in a situation where O ₂ remains on the exhaust side electrode of the air-fuel ratio sensor, the sum of (Do−Ki · Si · Di) of each combustible component i becomes a positive value. On the other hand, in a situation where O ₂ is insufficient on the exhaust side electrode of the air-fuel ratio sensor, in other words, in a situation where the combustible component i is surplus, the sum of (Do−Ki · Si · Di) of each combustible component i is negative. Value.

  Then, according to the above equation, the deviation amount IL is obtained when the fuel used is an alcohol X% fuel with respect to the output current IP1 (0) when the fuel used is a fuel of alcohol 0% (gasoline 100%). It is calculated as a deviation amount of the output current IP1 (X). Specifically, when the deviation amount IL calculated by the above equation becomes a positive value, the output current of the air-fuel ratio sensor may be corrected to the rich side. On the other hand, when the deviation amount IL calculated by the above equation becomes a negative value, the output current of the air-fuel ratio sensor may be corrected to the lean side. As described above, the output current of the air-fuel ratio sensor is corrected according to the deviation amount IL calculated by the above formula, and the fuel injection caused by the deviation amount is performed by performing the air-fuel ratio feedback correction based on the corrected output current. It becomes possible to suppress deterioration of control.

  According to the alcohol concentration estimation apparatus of the present invention, the alcohol concentration of the fuel used is estimated based on the difference between the output currents correlated with the moisture concentration in the exhaust gas. Therefore, the alcohol concentration is based only on the first output current. Compared with the case of estimating the alcohol concentration, the alcohol concentration can be estimated with high accuracy. That is, even if the first output current fluctuates due to the difference in the concentration (component ratio) of the combustible component in the exhaust gas, it is possible to suppress the deterioration in the estimation accuracy of the alcohol concentration due to this. In addition, the alcohol concentration can be estimated easily in a short time by simply raising the applied voltage to the air-fuel ratio sensor from the first applied voltage to the second applied voltage temporarily.

  According to the fuel injection control device for an internal combustion engine of the present invention, the deviation amount of the first output current of the air-fuel ratio sensor is accurately determined by using the alcohol concentration of the fuel used which is accurately estimated by the alcohol concentration estimation device. It becomes possible to calculate. This makes it possible to make the output current of the air-fuel ratio sensor corrected based on the deviation amount as close as possible to a value corresponding to the actual air-fuel ratio. Then, by performing the air-fuel ratio feedback correction based on the corrected output current, it is possible to suppress the deterioration of the fuel injection control due to the deviation amount.

1 is a diagram schematically showing a schematic configuration of an engine to which the present invention is applied. It is a figure which shows typically only 1 cylinder of the engine of FIG. It is a block diagram which shows the structure of the control system of an engine. It is sectional drawing which shows schematic structure of an air fuel ratio sensor. It is a figure which shows the voltage-current characteristic of an air fuel ratio sensor. It is a flowchart which shows an example of ethanol concentration estimation control. It is a flowchart which shows an example of fuel injection control. It is a table | surface which shows the molecular weight, oxygen equivalent ratio, etc. of each combustible component in exhaust gas. It is a figure which shows the relationship between the molecular weight of each combustible component in exhaust gas, and an oxygen equivalent ratio.

  Embodiments of the present invention will be described with reference to the accompanying drawings.

-Engine-
First, a schematic configuration of a flexible fuel internal combustion engine (engine) will be described with reference to FIGS. 1 and 2. FIG. 2 shows only the configuration of one cylinder of the engine.

  As shown in FIGS. 1 and 2, the engine 1 is a port injection type four-cylinder engine mounted on an FFV, and ethanol-containing fuel is used. Here, the ethanol-containing fuel is meant to include 100% gasoline fuel, a mixed fuel in which ethanol and gasoline are mixed, and 100% ethanol fuel.

  The engine 1 includes a cylinder block 1a formed with four cylinders # 1, # 2, # 3, and # 4 arranged in a line, and a cylinder head 1b attached to the upper end of the cylinder block 1a. Each cylinder # 1, # 2, # 3, and # 4 is provided with a piston 1c that reciprocates in the vertical direction. The piston 1c is connected to the crankshaft 15 via the connecting rod 16, and the reciprocating motion of the piston 1c is converted into the rotational motion of the crankshaft 15 by the connecting rod 16.

  A signal rotor 17 is attached to the crankshaft 15. A plurality of teeth (protrusions) 17 a are provided on the outer peripheral surface of the signal rotor 17 at equal angles (for example, 10 ° CA (crank angle)). The signal rotor 17 has a missing tooth portion 17b in which two teeth 17a are missing.

  A crank position sensor 31 that detects a crank angle is disposed near the side of the signal rotor 17. The crank position sensor 31 is an electromagnetic pickup, for example, and generates a pulsed signal (voltage pulse) corresponding to the teeth 17a of the signal rotor 17 when the crankshaft 15 rotates. Further, a water temperature sensor 32 for detecting the temperature of the engine cooling water is disposed in the cylinder block 1a.

  Below the cylinder block 1a, an oil pan 18 for storing lubricating oil is provided. Lubricating oil stored in the oil pan 18 is pumped up by an oil pump (not shown) through an oil strainer that removes foreign matters during operation of the engine 1, and the piston 1 c, crankshaft 15, connecting rod 16, etc. It is supplied to each part of the engine 1 and used for lubrication and cooling of each part. The lubricating oil is returned to the oil pan 18 after lubrication / cooling of each part of the engine 1 and stored in the oil pan 18 until it is pumped up again by the oil pump.

  A combustion chamber 1d is formed between the cylinder head 1b and the piston 1c. A spark plug 3 is disposed in the combustion chamber 1d. The ignition timing of the spark plug 3 is adjusted by the igniter 4. The igniter 4 is controlled by an ECU (Electronic Control Unit) 200.

  An intake passage 11 and an exhaust passage 12 are connected to the combustion chamber 1d. A part of the intake passage 11 is formed by an intake port 11a and an intake manifold 11b. A surge tank 11 c is provided in the intake passage 11. The intake passage 11 includes an air cleaner 7 for filtering intake air, a hot-wire air flow meter 33, an intake air temperature sensor 34 (built in the air flow meter 33), a throttle valve 5 for adjusting the intake air amount of the engine 1, and the like. Has been placed. The throttle valve 5 is provided on the upstream side of the surge tank 11 c (upstream side of the intake flow) and is driven by the throttle motor 6. The opening degree of the throttle valve 5 is detected by a throttle opening degree sensor 35. The throttle opening of the throttle valve 5 is driven and controlled by the ECU 200.

A part of the exhaust passage 12 is formed by an exhaust port 12a and an exhaust manifold 12b. A three-way catalyst 8 is disposed in the exhaust passage 12. In the three-way catalyst 8, CO in the exhaust gas exhausted to the exhaust passage 12 from the combustion chamber 1d, oxidation of HC, and NOx in the reduction is carried out, they CO _2, H ₂ O, to a N ₂ As a result, exhaust gas is purified.

  An air-fuel ratio (A / F) sensor 80 is disposed upstream of the three-way catalyst 8 in the exhaust passage 12 (upstream side of the exhaust flow). The air-fuel ratio sensor 80 generates a sensor output (output current) corresponding to the oxygen concentration of the exhaust gas flowing into the three-way catalyst 8. Details of the air-fuel ratio sensor 80 will be described later.

An O ₂ sensor 38 is disposed on the exhaust passage 12 downstream of the three-way catalyst 8. The O ₂ sensor 38 determines whether the exhaust gas is rich or lean based on the oxygen concentration of the exhaust gas flowing out from the three-way catalyst 8. Specifically, the O ₂ sensor 38 generates an electromotive force according to the oxygen concentration in the exhaust gas, and is determined to be rich when the output is higher than a voltage (comparison voltage) corresponding to the theoretical air-fuel ratio. On the contrary, when the output is lower than the comparison voltage, it is determined as lean.

  An intake valve 13 is provided between the intake passage 11 and the combustion chamber 1d. By opening and closing the intake valve 13, the intake passage 11 and the combustion chamber 1d are communicated or blocked. Further, an exhaust valve 14 is provided between the exhaust passage 12 and the combustion chamber 1d, and the exhaust passage 12 and the combustion chamber 1d are communicated or blocked by opening and closing the exhaust valve 14. The opening and closing drive of the intake valve 13 and the exhaust valve 14 is performed by each rotation of the intake camshaft 21 and the exhaust camshaft 22 to which the rotation of the crankshaft 15 is transmitted via a timing chain or the like.

  In the vicinity of the intake camshaft 21, a cam position sensor 39 is provided that generates a pulse signal when the piston 1c of a specific cylinder (for example, cylinder # 1) reaches the compression top dead center (TDC). . The cam position sensor 39 is, for example, an electromagnetic pickup, and is disposed so as to face one tooth (not shown) on the outer peripheral surface of the rotor provided integrally with the intake camshaft 21. When 21 rotates, a pulse-like signal (voltage pulse) is output. The intake camshaft 21 and the exhaust camshaft 22 rotate at a rotational speed that is 1/2 that of the crankshaft 15. Therefore, each time the crankshaft 15 rotates twice (720 ° CA rotation), one cam position sensor 39 is provided. Generates a pulsed signal.

  In the intake port 11a of the intake passage 11, an injector (fuel injection valve) 2 capable of injecting ethanol-containing fuel is disposed. The injector 2 is provided for each cylinder # 1 to # 4. The injectors 2 of the cylinders # 1 to # 4 are connected to a common delivery pipe 101. The fuel stored in the fuel tank 104 of the fuel supply system 100 is supplied to the delivery pipe 101, whereby the fuel is injected from the injector 2 into the intake port 11 a.

  The fuel injected from the injector 2 is mixed with intake air to become an air-fuel mixture, and is introduced into the combustion chamber 1d when the intake valve 13 is opened. The air-fuel mixture (fuel + air) introduced into the combustion chamber 1d is ignited by the spark plug 3 and combusted / exploded. Due to the combustion / explosion of the air-fuel mixture in the combustion chamber 1d, the piston 1c reciprocates and the crankshaft 15 rotates. The combustion gas generated by the combustion of the air-fuel mixture is discharged into the exhaust passage 12 as exhaust gas when the exhaust valve 14 is opened.

  The fuel supply system 100 includes a delivery pipe 101 commonly connected to the injectors 2 of the cylinders # 1 to # 4, a fuel supply pipe 102 connected to the delivery pipe 101, a fuel pump (for example, an electric pump) 103, and a fuel tank 104. Etc. The fuel tank 104 stores an ethanol-containing fuel having a predetermined ethanol concentration. Then, by driving the fuel pump 103, the fuel stored in the fuel tank 104 is supplied to the delivery pipe 101 via the fuel supply pipe 102. The drive control of the fuel pump 103 is performed by the ECU 200. Fuel is supplied to the injectors 2 of the cylinders # 1 to # 4 by the fuel supply system 100 having such a configuration.

-ECU-
Next, the ECU 200 that controls the operating state of the engine 1 configured as described above will be described with reference to FIG.

  As shown in FIG. 3, the ECU 200 includes a CPU 201, a ROM 202, a RAM 203, a backup RAM 204, and the like.

  The ROM 202 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 201 executes various arithmetic processes based on various control programs and maps stored in the ROM 202. The RAM 203 is a memory that temporarily stores calculation results in the CPU 201, data input from various sensors, and the like. The backup RAM 204 is a non-volatile memory that stores data to be saved when the engine 1 is stopped, for example. It is.

  The CPU 201, ROM 202, RAM 203, and backup RAM 204 are connected to each other via a bidirectional bus 207 and to an input interface 205 and an output interface 206.

The input interface 205 includes a crank position sensor 31, a water temperature sensor 32, an air flow meter 33, an intake air temperature sensor 34, a throttle opening sensor 35, an accelerator opening sensor 36 that outputs a detection signal corresponding to the depression amount of the accelerator pedal, and an O Various sensors such as a _2- sensor 38, a cam position sensor 39, and an air-fuel ratio sensor 80 are connected. In addition, the ignition switch 40 is connected to the input interface 205, and when the ignition switch 40 is turned on, cranking of the engine 1 by a starter motor (not shown) is started.

  The output interface 206 is connected to the injector 2, the igniter 4 of the spark plug 3, the throttle motor 6 of the throttle valve 5, the fuel pump 103 of the fuel supply system 100, and the like. The ECU 200 executes various controls of the engine 1 including “ethanol concentration estimation control” and “fuel injection control”, which will be described later, based on the detection signals of the various sensors described above.

-Air-fuel ratio sensor-
Next, the air-fuel ratio (A / F) sensor 80 will be described with reference to FIGS.

  In this embodiment, as the air-fuel ratio sensor 80, for example, a limit current type sensor having output characteristics (voltage-current characteristics) as shown in FIG. 5 is used. For example, the air-fuel ratio sensor 80 is configured as shown in FIG.

  As shown in FIG. 4, the air-fuel ratio sensor 80 includes a sensor element 81, an air-permeable inner cover 87 and an outer cover 88.

  The sensor element 81 includes a plate-shaped solid electrolyte layer (for example, made of zirconia) 82, an atmosphere side electrode (for example, a platinum electrode) 83 formed on one surface of the solid electrolyte layer 82, and the other surface of the solid electrolyte layer 82. The exhaust-side electrode (for example, platinum electrode) 84 and the diffusion layer (for example, porous ceramic) 85 formed are formed.

  The atmosphere side electrode 83 of the sensor element 81 is disposed in the atmosphere duct 86. The atmosphere duct 86 is open to the atmosphere, and the atmosphere flowing into the atmosphere duct 86 contacts the atmosphere side electrode 83. On the other hand, the surface of the exhaust side electrode 84 is covered with the diffusion layer 85, and a part of the exhaust gas flowing through the exhaust passage 12 passes through the inside of the diffusion layer 85 and contacts the exhaust side electrode 84. The exhaust gas passes through the small hole 88a of the outer cover 88 and the small hole 87a of the inner cover 87 and reaches the sensor element 81 (exhaust side electrode 84).

  The air-fuel ratio sensor 80 incorporates a heater 89 for heating the sensor element 81. The heater 89 is composed of a linear heating element that generates heat when energized from an in-vehicle battery power source, and heats the entire sensor element 81 by the heat generated by the heating element.

In the air-fuel ratio sensor 80 having such a configuration, when a predetermined voltage is applied between the atmosphere-side electrode 83 and the exhaust-side electrode 84, the concentration of O _{2 in} the exhaust gas is applied to the air-fuel ratio sensor 80 by this voltage application. An output current corresponding to (oxygen concentration) is generated.

More specifically, when the air-fuel ratio of the exhaust gas is lean, surplus O ₂ in the exhaust gas is received and ionized by an electrode reaction at the exhaust side electrode 84. When the oxygen ions move in the solid electrolyte layer 82 from the exhaust side electrode 84 to the atmosphere side electrode 83 and reach the atmosphere side electrode 83, the electrons are desorbed there and returned to O ₂ and discharged to the atmosphere duct 86. The By such movement of oxygen ions, a current (positive current) flows in the direction from the atmosphere side electrode 83 to the exhaust side electrode 84.

On the other hand, when the air-fuel ratio of the exhaust gas is rich, contrary to the above-described lean case, O ₂ in the atmospheric duct 86 receives ions by the electrode reaction at the atmospheric side electrode 83 and is ionized. The oxygen ions move in the solid electrolyte layer 82 from the atmosphere-side electrode 83 to the exhaust-side electrode 84 and then combusted components in the exhaust gas (for example, H ₂ , CO, CO ₂ and H ₂ O are produced by the catalytic reaction with HC and the like. By such movement of oxygen ions, a current (negative current) flows in the direction from the exhaust side electrode 84 to the atmosphere side electrode 83.

  The voltage-current characteristics of the air-fuel ratio sensor 80 are as shown in FIG. 5, for example. FIG. 5 is a diagram showing the relationship between the applied voltage VP applied between the atmosphere-side electrode 83 and the exhaust-side electrode 84 of the air-fuel ratio sensor 80 and the output current IP that is the sensor output. In FIG. 5, the characteristic when the fuel used is 100% gasoline and the air-fuel ratio is stoichiometric (theoretical air-fuel ratio) is shown by a solid line, and the fuel used is 100% ethanol fuel and the air-fuel ratio is stoichiometric. These characteristics are indicated by broken lines.

  As shown in FIG. 5, the voltage-current characteristic of the air-fuel ratio sensor 80 is a region where the output current IP hardly changes even when the applied voltage VP to the air-fuel ratio sensor 80 is changed (a limit voltage). A basin Z1 and a water splitting zone Z2) exist.

  The limit current region Z1 of the air-fuel ratio sensor 80 is a region that outputs a substantially constant current (limit current) IP1 corresponding to the oxygen concentration in the exhaust gas, and the oxygen concentration (air-fuel ratio) of the exhaust gas when the engine 1 is in operation. This is an area used to detect. The output current (first output current) IP1 in the limit current region Z1 changes according to the oxygen concentration of the exhaust gas. Specifically, as shown in FIG. 5, the output current IP1 increases as the air-fuel ratio of the exhaust gas becomes leaner, and conversely, the output current IP1 decreases as the air-fuel ratio of the exhaust gas becomes richer. . In the example of FIG. 5, when the fuel used is 100% gasoline and the air-fuel ratio is stoichiometric, the output current IP1 (IP1g) in the limit current region Z1 is set to 0 (mA) (stoichiometric). output).

Further, the output current IP1 in the limit current region Z1 changes according to the ethanol concentration of the fuel used. That is, as already described, if the ethanol concentration of the fuel used is different, the concentration (component ratio) of the combustible component in the exhaust gas will be different, and the output current IP1 in the limit current region Z1 will be different depending on the concentration of the combustible component. fluctuate. In this embodiment, ethanol is used as the alcohol. As the ethanol concentration of the fuel used increases, the concentration of H _{2 in} the exhaust gas increases, and the output current IP1 in the limit current region Z1 tends to shift to the rich side. is there. For this reason, as shown in FIG. 5, as the ethanol concentration of the fuel used increases, the output current IP1 in the limit current region Z1 decreases. Specifically, the output current IP1 in the limit current region Z1 is the maximum current IP1g when the fuel used is 100% gasoline, and the minimum current IP1e when the fuel used is 100% ethanol. When the fuel used is a mixed fuel in which ethanol and gasoline are mixed, the output current IP1 in the limit current region Z1 can take a value between the minimum current IP1e and the maximum current IP1g according to the ethanol concentration.

  On the other hand, when the applied voltage VP to the air-fuel ratio sensor 80 becomes lower than the minimum voltage VP1min in the limit current region Z1, the output current IP of the air-fuel ratio sensor 80 becomes smaller than the output current IP1 in the limit current region Z1. In this case, as the applied voltage VP decreases, the output current IP decreases approximately proportionally.

On the contrary, when the applied voltage VP to the air-fuel ratio sensor 80 becomes higher than the maximum voltage VP1max of the limit current region Z1, H ₂ O (water) in the exhaust gas is caused by zirconia or the like of the solid electrolyte layer 82 of the air-fuel ratio sensor 80. Since it is decomposed into H ₂ and O ₂ , the output current IP of the air-fuel ratio sensor 80 becomes larger than the output current IP1 in the limit current region Z1. That is, the output current IP of the air-fuel ratio sensor 80 is increased by electrolysis of H ₂ O contained in the exhaust gas.

  As shown in FIG. 5, as the applied voltage VP to the air-fuel ratio sensor 80 increases, the output current IP of the air-fuel ratio sensor 80 increases. When the applied voltage VP becomes equal to or higher than a predetermined voltage (VP2min), the applied voltage Even if VP is changed, the output current IP hardly changes and becomes a substantially constant value IP2. A region where the moisture in the exhaust gas is decomposed and a substantially constant current IP2 is output is referred to as a water decomposition region Z2. The output current (second output current) IP2 of the water splitting region Z2 is larger than the output current IP1 of the limit current region Z1 described above. Note that when the applied voltage VP to the air-fuel ratio sensor 80 becomes larger than a predetermined voltage (VP2max), the output current IP of the air-fuel ratio sensor 80 increases again.

-Ethanol concentration estimation control-
Next, ethanol concentration estimation control for estimating the ethanol concentration of the fuel used in the engine 1 will be described with reference to the flowchart of FIG. The routine shown in the flowchart of FIG. 6 relates to the ethanol concentration estimation control executed by the ECU 200, and is repeated at regular intervals.

  First, in step ST11, the ECU 200 applies an applied voltage VP to be applied between the atmosphere-side electrode 83 and the exhaust-side electrode 84 of the air-fuel ratio sensor 80 to a voltage within the limit current range Z1 (first applied voltage). Set to VP1 (VP1min ≦ VP1 ≦ VP1max). The voltage VP1 is set to 0.3 to 0.4V, for example. Subsequently, the ECU 200 acquires the output current IP of the air-fuel ratio sensor 80 in step ST12. At this time, the output current (first output current) IP1 in the limit current region Z1 is acquired.

  Next, in step ST13, the ECU 200 sets the applied voltage VP to the air-fuel ratio sensor 80 to a voltage (second applied voltage) VP2 within the range of the water splitting region Z2 (VP2min ≦ VP2 ≦ VP2max). That is, the voltage VP applied to the air-fuel ratio sensor 80 is increased from the voltage VP1 within the limit current region Z1 to the voltage VP2 within the water decomposition region Z2. This voltage VP2 is set to 0.6 to 0.8 V, for example. Subsequently, the ECU 200 acquires the output current IP of the air-fuel ratio sensor 80 in step ST14. At this time, the output current (second output current) IP2 of the water splitting zone Z2 is acquired.

  Next, in step ST15, the ECU 200 obtains a difference ΔIP (= IP2−IP1) between the output current IP2 of the water splitting region Z2 and the output current IP1 of the limit current region Z1. In step ST16, the ECU 200 estimates the ethanol concentration of the fuel used based on the output current difference ΔIP obtained in step ST15. In this case, the relationship between the output current difference ΔIP and the ethanol concentration of the fuel used is obtained in advance through experiments and calculations, and stored in the ROM 202 of the ECU 200 as a map (concentration estimation map). By doing so, it is possible to estimate the ethanol concentration of the fuel used.

The estimation of the ethanol concentration in step ST16 will be described in detail. The difference ΔIP in output current obtained in step ST15 is an increase in the output current IP of the air-fuel ratio sensor 80 that is increased by the decomposition of H ₂ O in the exhaust gas. Therefore, the difference ΔIP in the output current is an amount having a correlation with the H ₂ O concentration (moisture concentration) in the exhaust gas, and changes according to the moisture concentration in the exhaust gas.

  Here, the moisture concentration in the exhaust gas varies depending on the ethanol concentration of the fuel used. For example, according to the following formula (1), when 100% gasoline fuel burns, the moisture concentration in the exhaust gas is 12.0%.

2C ₁₀ H ₁₈ + 29O ₂ + 111.77N ₂ → 20CO ₂ + 18H ₂ O + 111.77N ₂ (1)
Further, according to the following equation (2), when 100% ethanol fuel burns, the moisture concentration in the exhaust gas is 18.1%.

C ₂ H ₅ OH + 3O ₂ + 11.56N ₂ → 2CO ₂ + 3H ₂ O + 11.56N ₂ (2)
The moisture concentration in the exhaust gas has a minimum value when the fuel used is 100% gasoline, and has a maximum value when the fuel used is 100% ethanol. Further, when the fuel used is a mixed fuel in which ethanol and gasoline are mixed, the moisture concentration in the exhaust gas can take a value between the minimum value and the maximum value according to the engine concentration.

  Thus, since the moisture concentration in the exhaust gas changes according to the ethanol concentration of the fuel used, the output current difference ΔIP changes according to the ethanol concentration of the fuel used, and increases as the ethanol concentration increases. Specifically, as shown in FIG. 5, the output current difference ΔIP is the minimum value ΔIPg when the fuel used is 100% gasoline, and the maximum when the fuel used is 100% ethanol. The value ΔIPe is obtained. When the fuel used is a mixed fuel in which ethanol and gasoline are mixed, the output current difference ΔIP can take a value between the minimum value ΔIPg and the maximum value ΔIPe according to the ethanol concentration.

  As described above, in this embodiment, the ethanol concentration of the fuel used is estimated based on the difference ΔIP in the output current that correlates with the moisture concentration in the exhaust gas. Therefore, based on only the output current IP1 in the limit current region Z1. Therefore, the ethanol concentration can be estimated with higher accuracy than when the ethanol concentration is estimated. That is, even if the output current IP1 in the limit current region Z1 fluctuates as described above, it is possible to suppress the deterioration of the estimation accuracy of the ethanol concentration due to this. In addition, the ethanol concentration can be easily estimated in a short time by simply increasing the voltage VP applied to the air-fuel ratio sensor 80 from the voltage VP1 within the limit current region Z1 to the voltage VP2 within the water splitting region Z2. can do.

-Fuel injection control-
Next, the fuel injection control of the engine 1 performed using the ethanol concentration of the fuel used estimated by the above-described ethanol concentration estimation control will be described.

  In this embodiment, the ECU 200 maintains the air-fuel ratio of the air-fuel mixture of the cylinders # 1 to # 4 at the target air-fuel ratio (for example, the theoretical air-fuel ratio) based on the outputs of the various sensors described above. The fuel injection amount of the injectors 1 to # 4 is controlled. Specifically, the ECU 200 calculates a fuel injection amount (basic fuel injection amount) that is a basis of the fuel injection amount of the injectors 2 of the cylinders # 1 to # 4, and the air-fuel ratio with respect to the calculated fuel injection amount. The final fuel injection amount is determined by performing feedback correction.

  The basic control of the air-fuel ratio feedback correction is conventionally known and will be briefly described here. The basic fuel injection amount is the current engine 1 such as the intake air amount (detected by the air flow meter 33), the engine speed (calculated based on the output from the crank position sensor 31), the coolant temperature (detected by the water temperature sensor 32), and the like. It is calculated based on a parameter indicating the operating state. Then, on the basis of the deviation between the actual air-fuel ratio according to the oxygen concentration in the exhaust gas detected by the air-fuel ratio sensor 80 and the target air-fuel ratio, each cylinder # The fuel injection amounts of the injectors 1 to # 4 are feedback-controlled. Specifically, when the actual air-fuel ratio is richer than the target air-fuel ratio, the fuel injection amounts of the injectors 2 of the cylinders # 1 to # 4 are corrected to decrease. Conversely, when the actual air-fuel ratio is leaner than the target air-fuel ratio, the fuel injection amounts of the injectors 2 of the cylinders # 1 to # 4 are corrected to be increased.

  In the fuel injection control of this embodiment, in addition to such basic control of air-fuel ratio feedback correction, correction based on the deviation of the output current IP1 of the air-fuel ratio sensor 80 described above is performed. This fuel injection control will be described with reference to the flowchart of FIG. The routine shown in the flowchart of FIG. 7 relates to fuel injection control executed by the ECU 200, and is repeated at regular intervals.

  First, the ECU 200 executes an ethanol concentration estimation process in step ST21. In this ethanol concentration estimation process, the same processes as steps ST11 to S16 shown in FIG. 6 are performed. That is, the ethanol concentration of the fuel used is estimated based on the difference ΔIP between the output current IP2 of the water splitting region Z2 of the air-fuel ratio sensor 80 and the output current IP1 of the limit current region Z1.

Subsequently, in step ST22, the ECU 200 calculates a deviation IL of the output current IP1 in the limit current region Z1 of the air-fuel ratio sensor 80 using the ethanol concentration of the used fuel obtained in step ST21. The deviation IL of the output current IP1 is the deviation of the output current IP1 in the limit current region Z1 with respect to the output current (output current corresponding to the actual air-fuel ratio) corresponding to the oxygen concentration in the exhaust gas. The output current IP1 changes according to the concentration (component ratio) of the combustible component in the exhaust gas. Examples of main combustible components in the exhaust gas when the ethanol-containing fuel burns include those shown in the table of FIG. In FIG. 8, as main combustible components in the exhaust gas, ten typical components (H ₂ , CH ₄ , CO, C ₂ H ₄ , C ₃ H ₆ , CH ₃ CHO, C ₃ H ₈ , C _{2 are used.} H ₅ OH, C ₆ H ₅ CH ₃ , C ₈ H ₁₈ ).

  The concentration of the combustible component in the exhaust gas when the ethanol-containing fuel burns varies depending on the ethanol concentration of the fuel used. In this embodiment, the relationship between the concentration of combustible components (including oxygen concentration) in the exhaust gas and the ethanol concentration of the fuel used is obtained in advance by experiments and calculations, and is mapped to the ROM 202 of the ECU 200 (combustible component map). I am trying to remember it. The concentration of the combustible component in the exhaust gas at the ethanol concentration is obtained by referring to the combustible component map in the ROM 202 based on the ethanol concentration estimated in step ST21. For example, for ethanol concentrations from 0% to 100%, a plurality of regions are set at equal intervals (for example, 10 regions at 10% intervals), and a combustible component map is created for each region and stored in the ROM 202. That's fine. The concentration of the combustible component in the exhaust gas corresponding to the ethanol concentration may be obtained by referring to the combustible component map corresponding to the region to which the ethanol concentration obtained in step ST21 belongs.

  In this embodiment, the deviation IL of the output current IP1 of the limit current region Z1 of the air-fuel ratio sensor 80 is calculated from the concentration of the combustible component in the exhaust gas obtained as described above. The output current IP1 is calculated by the following equation (3). Further, the deviation amount IL of the output current IP1 is calculated by the following equation (4).

IP1 = A · Dop = ΣA · (Do−Ki · Si · Di) (3)
IL = IP1 (X) −IP1 (0) (4)
From this equation (3), the output current IP1 when the used fuel is a fuel of ethanol X% is calculated. In this formula (3), “i” is a number (natural number) assigned to each combustible component in the exhaust gas for convenience (i = 1 to 10 in FIG. 8), and “Σ” is the exhaust gas. It is the sum total about each combustible component i in gas. “A” is a proportionality constant determined for each air-fuel ratio sensor 80. The proportionality constant A is a value determined according to the area of the exhaust-side electrode 84 of the air-fuel ratio sensor 80, and can be obtained in advance by experiments or the like. In this case, the proportionality constant A is set to a larger value as the area of the exhaust side electrode 84 is larger.

  Then, according to the equation (4), the deviation amount IL is obtained when the fuel used is a fuel of ethanol X% with respect to the output current IP1 (0) when the fuel used is a fuel of ethanol 0% (gasoline 100%). It is calculated as a deviation amount of the output current IP1 (X).

“Dop (%)” is the surplus oxygen concentration on the exhaust-side electrode 84 of the air-fuel ratio sensor 80. The surplus oxygen concentration Dop is a value representing the degree of excess or deficiency of O ₂ on the exhaust side electrode 84, as will be described later. In this embodiment, the surplus oxygen concentration Dop is the sum for each combustible component i in the exhaust gas of (Do-Ki.Si.Di), and the following "Do", "Ki", "Si" , And “Di”.

  “Do (%)” is the oxygen concentration in the exhaust gas flowing through the exhaust passage 12. On the other hand, “Di (%)” is an amount associated with the combustible component i in the exhaust gas flowing through the exhaust passage 12, specifically, the concentration of the combustible component i in the exhaust gas flowing through the exhaust passage 12. is there. As described above, the oxygen concentration Do in the exhaust gas and the concentration Di of the combustible component i in the exhaust gas can be obtained by referring to the combustible component map stored in the ROM 202 from the ethanol concentration estimated in step ST21. Is possible.

“Si” is an amount associated with the combustible component i in the exhaust gas passing through the diffusion layer 85 of the air-fuel ratio sensor 80. Specifically, “Si” is the oxygen equivalent ratio of the combustible component i in the exhaust gas when the output current IP1 of the air-fuel ratio sensor 80 is the same as the stoichiometric output (0 (mA) in this embodiment). The oxygen equivalent ratio Si is a value representing the ease (the ease of passage) when the combustible component i passes through the diffusion layer 85 of the air-fuel ratio sensor 80. In this case, the oxygen equivalent ratio Si is the ratio of the ease with which the combustible component i passes through the diffusion layer 85 to the ease with which O ₂ passes through the diffusion layer 85. The oxygen equivalent ratio Si can be obtained in advance by experiments or the like, and is a value unique to each combustible component i as shown in the table of FIG.

Here, there is a correlation between the molecular weight Mi of the combustible component i in the exhaust gas and the oxygen equivalent ratio Si. As shown in FIG. 8, when the combustible component i and O ₂ have substantially the same molecular weight (in the case of CO and C ₂ H ₄ in FIG. 8), the ease of passage through the diffusion layer 85 is the same as that of the combustible component i. O ₂ is substantially the same, and the oxygen equivalent ratio Si of the combustible component i is approximately 1. When the molecular weight of the combustible component i is smaller than O ₂ (in the case of H ₂ and CH _{4 in} FIG. 8), the combustible component i is easier to pass through the diffusion layer 85 than O ₂ , and the oxygen equivalent of the combustible component i The ratio Si becomes larger than 1. Conversely, when the molecular weight of the combustible component i is larger than that of O ₂ (in FIG. 8, C ₃ H ₆ , CH ₃ CHO, C ₃ H ₈ , C ₂ H ₅ OH, C ₆ H ₅ CH ₃ , C ₈ H ₁₈ ), the combustible component i is less likely to pass through the diffusion layer 85 than O ₂ , and the oxygen equivalent ratio Si of the combustible component i is smaller than 1.

Further, when the value of (molecular weight Mi) ^−1/2 of the combustible component i in FIG. 8 and the value of oxygen equivalent ratio Si are plotted on the graph of FIG. 9, the (molecular weight Mi) ^{−1/1 of} the combustible component i is plotted. There is a linear function relationship as shown by a straight line L between ² and the oxygen equivalent ratio Si. That is, there is a relationship represented by the following formula (5) (B and C are constants).

Si = B · Mi ^−1/2 + C (5)
The reason is considered that the diffusion coefficient when the combustible component i in the exhaust gas passes through the diffusion layer 85 of the air-fuel ratio sensor 80 is proportional to (molecular weight Mi) ^−1/2 . Therefore, by using this formula (5), it is possible to estimate the oxygen equivalent ratio of the combustible components other than those shown in FIG.

“Ki” is an amount associated with the combustible component i that reacts with O ₂ at the exhaust-side electrode 84 of the air-fuel ratio sensor 80, and specifically, is a chemical equivalent of the combustible component i in the exhaust gas. This chemical equivalent Ki is the number of moles of O ₂ required for complete combustion of 1 mole of combustible component i. The chemical equivalent Ki of the combustible component i is a value unique to each combustible component i. For example, when the combustible component i is H ₂ , the chemical equivalent Ki is ½, and the combustible component i is CO. The chemical equivalent Ki is ½.

From the above, (Do-Ki.Si.Di) of each combustible component i has the following values. Considering O ₂ and the combustible component i in the exhaust gas flowing through the exhaust passage 12, it is assumed that these O ₂ and the combustible component i pass through the diffusion layer 85 of the air-fuel ratio sensor 80 and reach the exhaust side electrode 84. . Then, it is assumed that O ₂ reaching the exhaust side electrode 84 reacts with the combustible component i. As a result, the value representing the amount (concentration) of O ₂ or combustible component i remaining (remaining) on the exhaust-side electrode 84 becomes (Do-Ki · Si · Di). (Do−Ki · Si · Di) takes a positive value when O ₂ remains on the exhaust side electrode 84, and conversely becomes a negative value when the combustible component i remains on the exhaust side electrode 84.

And the sum total of (Do-Ki * Si * Di) of each combustible component i becomes surplus oxygen concentration Dop. Therefore, the surplus oxygen concentration Dop is a value representing the degree of excess or deficiency of O ₂ on the exhaust side electrode 84 of the air-fuel ratio sensor 80. Specifically, in a situation where O ₂ remains on the exhaust-side electrode 84, the surplus oxygen concentration Dop becomes a positive value. In this case, the output current IP1 of the air-fuel ratio sensor 80 calculated by Expression (3) is a positive value. On the other hand, in a situation where O ₂ is insufficient on the exhaust side electrode 84, in other words, in a situation where the combustible component i is surplus, the surplus oxygen concentration Dop becomes a negative value. In this case, the output current IP1 of the air-fuel ratio sensor 80 calculated by the equation (3) is a negative value.

  Then, the deviation amount IL of the output current IP1 of the air-fuel ratio sensor 80 is calculated using the equation (4). At this time, IP1 (X) is a value calculated by equation (3) when the ethanol concentration estimated in step ST21 is X%, and IP1 (0) has an ethanol concentration of 0%. At a certain time, the value is calculated by equation (3).

  Then, as shown in FIG. 7, in step ST23, the ECU 200 corrects the fuel injection amount of the injector 2 of each cylinder # 1 to # 4 based on the deviation amount IL calculated in step ST22. In this case, the output current IP1 (actually measured value) of the limit current region Z1 of the air-fuel ratio sensor 80 is corrected based on the deviation amount IL, and the injectors 2 of the cylinders # 1 to # 4 are corrected based on the corrected output current IP1y. It is possible to correct the fuel injection amount. As the corrected output current IP1y, a value (IP1-IL) obtained by subtracting the deviation amount IL calculated by the equation (4) from the output current IP1 of the air-fuel ratio sensor 80 can be used.

  Specifically, when the deviation amount IL calculated by the equation (4) is a positive value, the output current IP1y is corrected to the rich side (side where the output current decreases) with respect to the output current IP1. On the contrary, when the deviation IL calculated by the equation (4) is a negative value, the output current IP1y is corrected to the lean side (the side where the output current increases) with respect to the output current IP1.

  As described above, in this embodiment, the deviation IL of the output current IP1 in the limit current region Z1 of the air-fuel ratio sensor 80 is accurately calculated by using the ethanol concentration of the used fuel accurately estimated in step ST21. It becomes possible to do. Explaining this point in detail, as described above, the deviation amount IL of the output current IP1 changes in accordance with the concentration of the combustible component i in the exhaust gas, and the concentration of the combustible component i in the exhaust gas depends on the concentration of the fuel used. It changes according to ethanol concentration. In this embodiment, since the ethanol concentration of the fuel used can be accurately estimated based on the difference ΔIP between the output current IP2 of the water splitting region Z2 of the air-fuel ratio sensor 80 and the output current IP1 of the limit current region Z1, the ethanol concentration Is used to calculate the deviation IL of the output current IP1. Therefore, the concentration of the combustible component i in the exhaust gas can be accurately obtained, and as a result, the deviation amount IL of the output current IP1 can be accurately calculated.

  As a result, the output current IP1y of the air-fuel ratio sensor 80 corrected based on the deviation amount IL can be brought as close as possible to a value corresponding to the actual air-fuel ratio. Then, by performing the air-fuel ratio feedback correction based on the corrected output current IP1y, it is possible to suppress the deterioration of the fuel injection control due to the deviation amount IL.

  In step ST22 described above, the concentration of the combustible component in the exhaust gas is obtained from the ethanol concentration estimated in step ST21, and the output current IP1 of the air-fuel ratio sensor 80 is obtained using the obtained concentration of the combustible component in the exhaust gas. However, the deviation amount IL of the output current IP1 of the air-fuel ratio sensor 80 may be directly obtained from the ethanol concentration estimated in step ST21. In this case, the relationship between the deviation amount IL and the ethanol concentration of the fuel used is obtained in advance by experiments and calculations, and stored in the ROM 202 of the ECU 200 as a map (deviation amount map), and this map is referred to. The deviation amount IL can be estimated.

-Other embodiments-
The present invention is not limited only to the above-described embodiments, and all modifications and applications within the scope of the claims and within the scope equivalent to the scope are possible.

  The ethanol-containing fuel as the fuel used in the above embodiment is an example, and other alcohol-containing fuel (for example, methanol-containing fuel) may be used as the fuel used in the flexible fuel internal combustion engine.

  The structure of the air-fuel ratio sensor described in the above embodiment (see FIG. 4) is an example, and any other structure may be used as long as it is a limiting current type air-fuel ratio sensor exhibiting characteristics as shown in FIG. Good.

  In the above embodiment, the case where the present invention is applied to a port injection type four-cylinder engine mounted on an FFV has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the present invention is not limited to a port injection type engine, but can be applied to an in-cylinder direct injection type engine and an engine including both a port injection type and an in-cylinder direct injection type injector. Further, the number of cylinders and the engine type (in-line type, V type, horizontally opposed type, etc.) are not particularly limited.

  INDUSTRIAL APPLICABILITY The present invention can be used for an alcohol concentration estimation apparatus for a flexible fuel internal combustion engine that uses an alcohol-containing fuel as a fuel. The present invention can also be used in a fuel injection control device for a flexible fuel internal combustion engine that uses an alcohol-containing fuel as a fuel.

1 Engine 1d Combustion chamber 2 Injector (fuel injection valve)
3 Spark plug 8 Three-way catalyst 11a Intake port 12 Exhaust passage 12a Exhaust port 13 Intake valve 14 Exhaust valve 80 Air-fuel ratio (A / F) sensor 100 Fuel supply system 200 ECU
IP1 first output current IP2 second output current ΔIP difference in output current VP1 first applied voltage VP2 second applied voltage

Claims (6)

A combustion chamber, an intake port and an exhaust port communicating with the combustion chamber, an intake valve and an exhaust valve capable of opening and closing the intake port and the exhaust port, a fuel injection valve capable of injecting fuel into the intake port or the combustion chamber, and combustion An internal combustion engine comprising an ignition plug that ignites an air-fuel mixture in the chamber and an air-fuel ratio sensor that is provided upstream of the catalyst disposed in the exhaust passage and detects the oxygen concentration in the exhaust gas and uses alcohol-containing fuel An alcohol concentration estimation device of
When the first applied voltage is applied, the air-fuel ratio sensor outputs a current corresponding to the oxygen concentration in the exhaust gas, and a second applied voltage higher than the first applied voltage is applied. When configured to decompose water contained in the exhaust gas,
Based on the difference between the second output current when the second applied voltage is applied and the first output current when the first applied voltage is applied, the alcohol concentration of the fuel used is estimated. An alcohol concentration estimation apparatus characterized by: The alcohol concentration estimation apparatus according to claim 1,
The alcohol estimation apparatus, wherein the alcohol is ethanol. A combustion chamber, an intake port and an exhaust port communicating with the combustion chamber, an intake valve and an exhaust valve capable of opening and closing the intake port and the exhaust port, a fuel injection valve capable of injecting fuel into the intake port or the combustion chamber, and combustion An internal combustion engine comprising an ignition plug that ignites an air-fuel mixture in the chamber and an air-fuel ratio sensor that is provided upstream of the catalyst disposed in the exhaust passage and detects the oxygen concentration in the exhaust gas and uses alcohol-containing fuel The fuel injection control device of
The alcohol concentration estimation apparatus according to claim 1 or 2,
Using the alcohol concentration estimated by the alcohol concentration estimation device, the deviation amount of the first output current with respect to the output current based on the oxygen concentration in the exhaust gas is calculated,
The first output current is corrected according to the calculated shift amount,
A fuel injection control device for an internal combustion engine, wherein the fuel injection amount by the fuel injection valve is controlled based on the corrected first output current. The fuel injection control device for an internal combustion engine according to claim 3,
From the alcohol concentration estimated by the alcohol concentration estimation device, obtain the concentration of the combustible component in the exhaust gas at the alcohol concentration,
A fuel injection control device for an internal combustion engine, wherein the calculated deviation amount of the first output current is calculated using the determined concentration of the combustible component in the exhaust gas. The fuel injection control device for an internal combustion engine according to claim 4,
The amount of deviation of the first output current is given by the following equation:
IL = IP1 (X) -IP1 (0)
(IL: shift amount of the first output current, IP1 (X): first output current when the fuel used is a fuel of alcohol X%, IP1 (0): fuel with a fuel used of 0% alcohol The first output current when
A fuel injection control device for an internal combustion engine, characterized by: The fuel injection control device for an internal combustion engine according to claim 5,
The first output current IP1 (X) when the fuel used is a fuel of alcohol X% is expressed by the following equation:
IP1 (X) = ΣA · (Do−Ki · Si · Di)
(A: proportional constant, Do: oxygen concentration in exhaust gas, i: number assigned to each combustible component in exhaust gas, Ki: chemical equivalent of combustible component i in exhaust gas, Si: output of air-fuel ratio sensor Oxygen equivalent ratio of combustible component i in exhaust gas when current is same as stoichiometric output, Di: concentration of combustible component i in exhaust gas)
A fuel injection control device for an internal combustion engine, characterized by:

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